Spin Flop, Supersolids, and Bicritical and Tetracritical Points

Abstract

A scaling theory is introduced for bicritical points, such as antiferromagnetic spinflop points (with analogies to the upper $\ensuremath{\lambda}$ point in $^{4}\mathrm{He}$), where two distinct critical lines meet. Experimentally testable predictions follow from renormalization-group calculations which indicate that the bicritical exponents should be Heisenberg like for systems with $n\ensuremath{\le}3$ components; the crossover exponent $\ensuremath{\varphi}(\ensuremath{\simeq}1.25 \mathrm{for} n=3)$ is directly observable. For $n>3$ an intermediate ("supersolid") low-temperature phase may appear, the bicritical point then becoming tetracritical.